1. Field of the Invention
The present invention relates to reciprocating piston electromagnetic fluid pumps, and in particular to a transistorized circuit for a reciprocating piston electromagnetic fluid pump.
2. Description of the Prior Art
Reciprocating piston electromagnetic fluid pumps as disclosed in the patent to Parker U.S. Pat. No. 2,994,792 (August, 1961) and Wertheimer et al., U.S. Pat. No. 3,381,616 (May, 1968) have obtained wide commercial acceptance, but in a highly competitive field, material and fabrication costs, and improvements in operation are very important. The early models of these pumps as represented by the one disclosed by Parker cited above included an electrical switch in circuit relationship with a solenoid coil which is either mechanically or magnetically actuated by the piston in the fully retracted or cocked position. Opening of the switch terminates the electrical power to the solenoid coil and the piston initiates its pumping stroke under the force of a cocked spring. Although this type of pump functions very satisfactorily and has a reasonable operational life, the switch is highly subject to failure and is determinative of the pump's operating life.
To increase the operational life of the pump, the use of the switch was abandoned and the art turned to blocking oscillators as taught by Wertheimer above. Blocking oscillators eliminated the switch problem but introduced the need for a sensing coil, increasing the complexity and cost of the pump. Unfortunately, blocking oscillators work fine only within limited temperature and voltage ranges, and outside the nominal ranges, starting problems were encountered. Temperature compensating networks using thermistos and voltage control networks using Zener diodes are presently being used to overcome these problems with limited success but have further increased the complexities and costs of the pumps as compared to the simple circuits disclosed by Wertheimer. The present invention combines the simplicity and reliability of the switch for assuring starting of the pump over a wide voltage and temperature range and the effectiveness of a solid state switch for trouble free switching of the current flow in the solenoid.